The long-term goal of this project is to reach a comprehensive understanding of aging in human somatosensation. The proposed studies will build upon the results from preceding years which have revealed, among other things, that somatosensory aging is progressive rather than precipitous, and pervasive rather than sporadic, even though its rate varies greatly among body sites and people. The general objectives of the proposed research are (1) to extend the study of tactile and thermal aging on different areas of the body, (2) to investigate key factors that may influence the rate and magnitude of somatosensory aging, and (3) to determine if declines in thermal and tactile perception are sufficient to pose health risks for older people. These objectives will be pursued via four specific aims: In Aim 1 we will study the effect of aging on vibrotaction across the body, with the goal of mapping changes in sensitivity to different frequencies of vibration that are mediated by different types of mechanoreceptors. In Aim 2 we will test the hypothesis that declining vascular function contributes to the deterioration of cutaneous sensitivity during aging. The association between tactile sensitivity and cutaneous and arterial blood flow will be determined for younger and older adults, with an emphasis on the possible effects in older adults of life-long habits of smoking and/or physical inactivity. In Aim 3 we will explore whether, as threshold tests in the previous grant period imply, the ability to sense innocuous warming and cooling can be so impaired by aging that it is effectively lost at some body sites. Such losses could reduce peripheral inputs to thermoregulatory mechanisms in old age. In Aim 4 we will study the neglected topics of tactile temporal perception and resolution, which may suffer as neural conduction and CNS processing slow with age. Slower temporal processing may in turn contribute to difficulties of balance and coordination among older people. Together these studies will provide new information about the nature and degree of somatosensory aging, its relationship to potentially important physiological and behavioral factors, and how it may affect health and well-being in senescence.